1. Field of the Invention
This invention relates to a laser irradiation apparatus, more particularly to a laser irradiation apparatus which irradiates a plurality of laser beams.
2. Description of the Prior Art
It is known that the interaction between a substance and a ray varies according to the wave-length of the ray and the property constants of materials irradiated with the ray. The constants include a reflectivity, absorption coefficient, scattering coefficient, thermal conductivity, and thermal diffusion constant. Particularly, the reflectivity, absorption coefficient and scattering coefficient have dependence on the wave-length.
For example, it is known that the absorption coefficient depends on various absorption factors in the material and in the case of solid materials, there can be mentioned basic absorption by interband transition, free electron absorption, grid absorption (phonon absorption), impurity absorption, and so on. These absorptions depend on the wave-length of ray inputs.
Also, in the case of a living organism, similar phenomenons occur. Water which is a predominant component of the living organism has an absorption band according to the vibration of water molecules in the infrared range. In the visible range, there exists absorption due to the presence of hemoglobin. Further, the scattering coefficient in a living organism is the factor which must be taken into consideration.
Thus, when a laser of a specific wave-length is irradiated on an object, the effect of the irradiation varies largely depending on the oscillation wave-length. For example, if a CO.sub.2 laser beam which has a wave-length of 1.6 .mu.m is irradiated onto a living organism, the laser beam does not scatter within the living organism, but is locally absorbed to cause incision and vaporization of the living organism. This is due to the fact that the absorption coefficient is as high as 200 cm.sup.-1 against the laser beam which has a wave-length of 10.6 .mu.m while the scattering coefficient is 0 (zero).
On the other hand, when a YAG laser beam which has a wave-length of 1.06 .mu.m is irradiated onto a living organism, the absorption coefficient of the living organism is as low as approximately 1/200 of the CO.sub.2 laser beam, but the scattering coefficient becomes as high as 10 cm.sup.-1 so that the laser beam penetrates into the living organism. Therefore, the YAG laser beam is known to be more suitable for coagulation of a living organism rather than for incision thereof.
An Ar laser beam which has a wave-length of 0.53 .mu.m has an absorption characteristic that it can be well absorbed by hemoglobin in the blood. An identical effect is realized by the second harmonics of the YAG laser beam of 0.503 .mu.m.
According to clinical data reported from various facilities, the CO.sub.2 laser cannot independently stop bleeding if the blood vessel diameter exceeds 1 mm. On the other hand, it is reported that the YAG laser does not have sufficient ability to perform an incision on a living organism.
Therefore, in laser surgery, it is almost impossible to carry out a bloodless operation by separately and independently using the CO.sub.2 surgical laser, the YAG surgical laser or the Ar surgical laser. It is desirable to irradiate a plurality of laser beams of different wave-lengths to produce a combination of different effects due to the different wave-lengths.
Conventionally, a proposal has been disclosed in Japanese Laid-Open Patent Applications No. 19136/80 and No. 81643/80, in which both the CO.sub.2 laser beam and the YAG laser beam are irradiated by a single apparatus. Thus, according to the prior arts, the apparatus irradiates a plurality of laser beams of different wave-lengths so as to effectively utilize the interaction of individual laser beams for medical treatments.
The above-mentioned prior arts disclose only that a plurality of laser beams are simply blended and irradiated. Therefore, the prior arts do not provide an apparatus which can perform medical treatment in the best condition for the various living organism and they cannot fully attain desired complex medical treatment effects, because each living organism requires a different type of medical treatment according to the local condition of the living organism and, therefore, requires specific blood-stopping action and vaporization of the living organism. Furthermore, in a particular case, the best laser output is determined according to the condition of the affected part of the living organism.
The conventionally known CO.sub.2 surgical laser apparatus normally consists of a CO.sub.2 laser resonator, output variation means for adjusting discharge current of the CO.sub.2 laser resonator, output variation signal means for controlling the output variation means, output setting means for setting oscillation outputs and a light guide for leading the laser beams from the resonator to desired positions.
Similarly, the conventionally known YAG surgical laser apparatus normally consists of a YAG laser resonator, output variation means for adjusting the exciting flash-lamp output of the YAG laser resonator, output variation signal means for controlling the output variation means, output setting means for setting ocsillation outputs and a light guide for leading the laser beams from the resonator to desired positions. Also, the conventional Ar surgical laser apparatus consists of similar components.